Population Genetics of Vibrio cholerae from Nepal in 2010: Evidence on the Origin of the Haitian Outbreak

Abstract

Cholera continues to be an important cause of human infections, and outbreaks are often observed after natural disasters, such as the one following the 2010 earthquake in Haiti. Once the cholera outbreak was confirmed, rumors spread that the disease was brought to Haiti by a battalion of Nepalese soldiers serving as United Nations peacekeepers. This possible connection has never been confirmed. We used whole-genome sequence typing (WGST), pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibility testing to characterize 24 recent Vibrio cholerae isolates from Nepal and evaluate the suggested epidemiological link with the Haitian outbreak. The isolates were obtained from 30 July to 1 November 2010 from five different districts in Nepal. We compared the 24 genomes to 10 previously sequenced V. cholerae isolates, including 3 from the Haitian outbreak (began July 2010). Antimicrobial susceptibility and PFGE patterns were consistent with an epidemiological link between the isolates from Nepal and Haiti. WGST showed that all 24 V. cholerae isolates from Nepal belonged to a single monophyletic group that also contained isolates from Bangladesh and Haiti. The Nepalese isolates were divided into four closely related clusters. One cluster contained three Nepalese isolates and three Haitian isolates that were almost identical, with only 1- or 2-bp differences. Results in this study are consistent with Nepal as the origin of the Haitian outbreak. This highlights how rapidly infectious diseases might be transmitted globally through international travel and how public health officials need advanced molecular tools along with standard epidemiological analyses to quickly determine the sources of outbreaks.

Genomic diversity of 2010 Haitian cholera outbreak strains

“…Although the molecular and genomic data in the previous reports cited here have been interpreted as being consistent with V. cholerae being introduced to Haiti by outside visitors (5,7,8), a definitive statement of source attribution cannot yet be made. To assess source attribution, a qualified reference database (including recent strains from Nepal, India, and Cameroon, and related V. cholerae strains from concurrent epidemics) representative of global phylogenetic diversity as well as well-documented population diversity within the heterogeneous clade and its near neighbor comparators, is critical.…”

CtxB1 outcompetes CtxB7 in Vibrio cholerae O1, Bangladesh

“…Recent studies revealed the V. cholerae O1 ET associated with cholera outbreaks in Haiti to be genetically closely related to ET strains associated with cholera in Asia (Hendriksen et al, 2011). Based on single nucleotide polymorphism (SNP) analysis of the V. cholerae genome, the seventh cholera pandemic was shown to be transmitting worldwide via three major overlapping waves from the Ganges Delta of the Bay of Bengal, the historical home of Asiatic cholera (Mutreja et al, 2011).…”

Molecular tracing of the emergence, adaptation, and transmission of hospital-associated methicillin-resistant Staphylococcus aureus

“…Comparative genomic analysis of closely related isolates from epidemics occupying different niches or associated with different disease manifestations is a powerful means for identifying genetic events that may have contributed to clone emergence and pathogenesis (23,(25)(26)(27). PVL has been a marker for community-associated clones of S. aureus associated with skin and soft tissue infections or severe necrotizing pneumonia (28), although increased identification of PVL + strains associated with nosocomial infections weakens this correlation (29,30).…”